X-Ray Binaries: A Potential Dominant Contributor to the Cosmic-Ray Spectral Knee Structure

Abstract “PeVatrons” refer to astrophysical sources capable of accelerating particles to energies of ∼PeV and higher, potentially contributing to the cosmic-ray spectrum in the knee region. Recently, the High-Altitude Water Cherenkov Observatory (HAWC) and the Large High Altitude Air Shower Observatory (LHAASO) have discovered a new type of PeVatron–X-ray binary, allowing us to investigate in greater depth the contributions of these sources to cosmic rays around the knee region. There are hundreds of X-ray binaries observed in our Galaxy that are potential PeVatrons. In this work, we derive the radial distribution of X-ray binaries in the Galaxy. Then we use the DRAGON package to calculate energy spectrum, anisotropy of cosmic rays, and the resulting diffuse gamma-ray emissions, after considering them as factories of cosmic rays in the knee energy bands. Our findings show that the contributions from X-ray binary PeVatrons may be dominant. More X-ray binary PeVatrons can be observed by LHAASO and HAWC in the future and will confirm the contribution of X-ray binaries to high-energy cosmic rays.